Animation and modelling workflow
Blender has a very flexible workflow, and you can do things in virtually any order and get away with it without too much extra work. I don't think it is industry standard to sculpt twice, but that should not stop you from doing it if you have to.


This really does not matter, you can either bake the normals first or rig the model. None depends on the other.
I don't really see the need for sculpting again after a pose. The only reason I could imagine (assuming you are talking about character modeling here) going back to bake a new normal map is if you modeled in a stiff T-pose and then decide you need some more details in areas that were stretched in the unrigged model. It would thus make sense to sculpt over those areas again after the pose is changed.
Shape keys can be used to animate the shape of a model in addition to bones. These would surely be made by the sculptor. Again, in blender the order of doing the rig and adding shape keys is irrelevant. You just need a retopoed model to work with.


Hope that helped!